Loosely translated, Sudoku means 'Single Numbers'. The objective of the Game is to enter the numbers 1-9 in each row, column and region of 3 X 3 cages, without repeating a number. This is the only rule. The level of difficulty of each game correlates to the number of spaces which need to be filled in. The more spaces, the more difficult a game is.

Take a look at this Game Board for example. There's only one Game in this example.

You can clearly see the only missing number from the top row is the number 7. So you can safely enter the number 7 to complete the top row. However, working out which numbers belong in the bottom row takes some effort.